Why? The entire Tell Tale Team would then need to learn how to create games in the source engine. They would have to learn about animating in faceposer rather then just exporting all their stuff from 3dsmax into the game, not to mention all the work they would have to do just to build the poker game mechanics in source.

As far as I know learning faceposing on the Source engine is quite easy, especially with a Dev Team, And I’m pretty sure that building the poker mechanics for Source wouldn’t be much harder than building the poker mechanics for the original game.
Anyway, Nice game, they only need to fix the animation on ‘Beat me three times’ and the game would be perfect then.